The present disclosure generally relates to varying focus and prescription correction in virtual and augmented reality systems, and specifically relates to a varifocal system within a head-mounted display (HMD) that includes a modular air spaced optical assembly.
Head-mounted displays (HMDs) typically are setup for uncorrected vision, and then require the end-user to wear contacts, or if small/viable enough, wear their prescription correction glasses within the HMD. Given the distribution of possible optical errors (primarily decomposed into spherical and astigmatism), there is a very large number of combinations present and a significant user-base that is not able to adequately wear their glasses. In addition, wearing unknown prescription or adding third-party optical elements introduces unknown optical elements and therefore distortion and focal cues into HMD based systems. This can cause the wrong distortion parameters, focus errors, reflections/scatter if an eye tracker is present in an HMD system, or general issues related to human factors, such as issues with comfort, weight, fit, etc.
One approach to solve the aforementioned problems is to allow a user wearing the HMD to swap or add optical elements to the HMD system that can correct for a user's optical prescription. However, given that optical prescriptions are usually specified in quarter-diopter ranges for power and astigmatism (which also includes rotation angle), there are literally thousands of combinations for correcting a user's optical prescription, which can make the logistics approach in HMD systems vary challenging. Furthermore, an approach based on applying calibration in HMD systems with third-party prescription optics, in order to remove distortion induced artifacts or eye tracking issues, is typically not accurate and efficient. Thus, it is desirable to efficiently implement optical prescription correction into HMD systems.